Three of them were clearly in really bad condition and there was no chance of having much better result, apart from Koln who failed because the match ended in a draw, there was also Mainz 05 who ended in draw against Heidenheim.
They are guaranteed to be eliminated from the Bundesliga and have to repeat the struggle to get promotion tickets in Bundesliga 2, clearly this is situation that will really make things difficult for all of them.
Just look at Bundesliga 2, currently it is full of quite strong team, even though those at the top will be promoted to the Bundesliga, several other teams will also definitely take advantage of the opportunity next season to get promoted.
Competition in Bundesliga 2 is very interesting and it is not easy to get the title or finish in the top position next season, I think they will be in Bundesliga 2 for longer time.

It really lucky for Mainz 05 considering they are only 1 point behind to get comfortable position in the Bundesliga by avoiding the relegation zone, besides that there is chance to survive by winning the play-off round.
But in the deciding match, I quite sure that Mainz 05 will win because their experience in the Bundesliga against big teams will be useful in being able to win the match and maintain their position as team in the Bundesliga competition.
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Koln probably does not have much chance of avoiding the relegation this season. And as you said, the Bundesliga 2 is also full of strong teams. So it is going to be hard for whichever team that gets relegated to actually get the promotion again.

Mainz does still have a chance though. The problem is they are going to play against Dortmund and Wolfsburg in the next two matches that are left for them in this season. And on the other hand, the team that they are actually trying to get ahead of, union Berlin, is going to play against Koln and Freiburg in the next two matches. So it does look like Mainz is going to find it hard to avoid relegation even though they are only one point behind Union Berlin